L9 Diffusive Gaseous Exchange Flashcards
Gaseous diffusion
Inhalation –> Excretion
Atmosphere -tidal volume-> Lung -gaseous exchange-> Circulation -gaseous exchange-> cell –> circulation –> Lung –> Atmosphere
-Diffusion drives the gas into the Mitochondria in the cell
-Diffusion: therefore entirely passive (no active transport) driven by difference in partial pressure
Driver of Gaseous diffusion
Gaseous diffusion of gas is driven by a difference of Partial pressure of the gas
Gaseous Diffusion
The partial pressure (P) of a dissolved (into the blood) gas
-the pressure required to prevent a gas from diffusing out of the solution is its partial pressure
-Soluble gas in solvent, molecules with upwards random motion. Weightless barrier/plunger. Downwards Force to overcome the escaping force of the molecules.
Pressure= Force spread over the area = F/A
-Partial pressure of a gas in solution has the same magnitude as the partial pressure of the gas in the air with which it is in equilibrium
Partial pressure
Dalton's Law PARTIAL because the barometric pressure is the sum of the different pressures of different elements PB = PN2 + PAr + PO2 + PH2O + ... PN2= 78% PO2= 21% PCO2= little bit PH2O= varies greatly
Partial pressure of gas in solution
The Partial pressure of a gas in solution has the same magnitude as the partial pressure of the gas in the air with which it is in equilibrium
(gas Partial pressure solution = /same as equilibrium air)
-if oxyHb is in equilibrium with oxygen in air, partial pressure of Oxygen will be 21%
(never truely 21% as there is alot of loss of partial pressure throughout the system)
Gaseous diffusion equilibrium
solution with solvent with gas dissolved in it. partial pressure in solution in equilibrium with partial pressure of gas above
–>
Removing air on top, place plunger on, and stopping the molecules from escaping with force applied on plunger
Gas Solubility
the AMOUNT of gas dissolved per unit of volume per unit of PARTIAL PRESSURE
sigma = C (content) / P (partial pressure)= axis
=HENRY’s Law
=molL-1 / kPA = mLL-1/mmHg
-increase partial pressure of gas in solution, will increase the content of that gas
-High solubility= for any given partial pressure, we will get more of that gas dissolved than if low solubility
-gradient= solubility
Oxygen and CO2 Solubility
High solubility= CO2 = 60mLL-1 (100mmHg)-1
Low Solubility= O2 = 3mLL-1 (100mmHg)-1
(per L of blood)
-CO2 is 20x more soluble in blood vs oxygen
(100mmHg is the partial pressure of O2 in blood (vs 21% partial pressure in air). for Barometric pressure of 760mmHg, 150mmHg partial pressure of O2 in room vs 100mmHg in lung))
-units: mLL-1 (mmHg)-1
Diffusion of Oxygen across the alveolar membrane
V.O2= rate of oxygen consumption = Volume O2/ delta(t) = VO2/delta(t)
=consumption creates the partial pressure gradient for diffusion to occur
-must be oxygen being consumed in capillaries
-consumption decreases the partial pressure, allowing gradient to be established
-V.O2 commonly measured at mouth
Diffusion of Oxygen across the alveolar membrane equation
VO2/delta(t) = V.O2 = D(o2) x A x ((solubility o2) x (PAo2 - PCo2))/d) D= diffusivity = inherent property of oxygen/ability to diffuse (different for every gas) A= area of pulmonary membranes available for exchange sigma= Solubility (if insoluble then nothing will go across) (PAo2-PcO2) = partial pressure gradient = driving force d= thickness= diffusion is inversely proportional V.O2 = D(L) (PAo2 - Pco2) where D(L) = Dgas x Solubility gas x (A/d) -only thing that matters is the partial pressure gradient (higher is being delivered through cylinder) -D(L) = Diffusing capacity of the lung= new constant combining the previous multiple constants -Dgas and Solubilitygas = both different for every gas = both aid diffusion and help to overcome oxygens low solubility -A and d will characteristic of the lung itself (A=100m2 (huge)) (d=300nm (very small))
D(L)
Diffusing capacity of the lung
Diffusive conductance of the lung
-conductance (quantity/time)
Effect of diffusion distance on diffusion time
distance something can diffusion depends on the SQUARE ROOT of time
(very slow process if distance is large)
Diffusion of O2 through protoplasm
-diffusion in terms of vessels
diffusivity= time to reach 90% saturation at centre of cylinder (from outside)
1cm= Low gradient as large distance = takes 11100 sec
7mm= steeper gradient = takes 54sec (nearly 1min)
7um= very steep gradient = 0.0054s
-diffusion is very fast over small distances, and very slow over large distances. due to square root relationship
Delivery of O2 to cell masses
-diffusion in terms of tissue
Diffusion: collection on cells relying on external diffusion = low gradient and low time to reach 90% equilibrium
Circulation= BV circulation around each cell= vastly reduce diffusion distance = reduce diffusion time
-Striated muscle= supply every cell with a supply of Oxygen
-diffusion is very fast over small distances, and very slow over large distances. due to square root relationship
Ways to decrease diffusion distance
- Decrease vessel diameter
2. Circulation around every cell (instead of having external diffusion)
Measurement of the Diffusion capacity equation
D(L(o2)) = rate of O2 pre unit time/ partial pressure gradient = V.O2/ (PAo2-PcO2)
O2 Proxy= D(L(CO)) = V.CO / PAco
Diffusion and disease
diffusion capacity is greatly reduced in many diseases
Measurement of the Diffusion capacity
CO is commonly used
1. Mimic’s Oxygen in its (low) solubility (proxy for oxygen)
2. CO + Hb –> HbCO
-Co binds with Hb with great avidity
-binds and stays bound to Hb until RBC is recycled in a few months
-bound but doesnt release into cell= therefore PcCO approx 0 (doesnt re-circulate)
irreversibly taken up to the Hb
hence:
D(L(CO)) = V.CO / PAco
Diffusion Limitation vs Perfusion Limitation
Time gas/Hb/CO spends in capillary = 0.75 sec (3/4)
-rate increases with exercise
PO2 start of capillary= 40mmHG = mixed blood from all over body (some low some high in PO2)
resting= send blood out saturate –> comes back only 1/2 saturated = allows for reservoir to tap into during exercise
-semi wasteful as sending O2 out and bringing 1/2 back
Diffusion Limitation vs Perfusion Limitation in disease
Abnormal O2 diffusion
- RBC wont be full saturated by the time (0.75 sec) it leaves the capillary
- early in line= death
Diffusion Limitation vs Perfusion Limitation Nitrous Oxide and CO
N2O= Nitrous oxide
fully saturated before even part way through the capillary (less than 0.25 sec)
CO= content stays very low as isnt be recirculated back/remains bound/irreversibly taken up to the Hb
Steady state/Rest Gas Exchange: e.g. O2
Mitochondria consumes oxygen in cell = decreases O2 partial pressure = driving gradient for consumption
1. Ventilation= Advection= bulk movement of gases = (V.O2= V.IO2 - V.EO2) (rate of oxygen consumption= difference between rate of inspiring and expiring Oxygen (reserve left over)
2. Diffusion (across alveolar-pulmonary capillary membrane) = V.O2= DL (PAo2 - Pco2)
3. Advection of O2 in blood (Circulation) (bulk carrying of O2 in fluid/blood)
=Ficks Law = V.O2 = Q (Cao2 - C-vo2) = rate O2 leaves blood = CO/Rate of flow of blood x (difference in O2 content (systemic arterial-mixed venous blood)
(rest= 40% of blood comes back without being used)
4. Diffusion of O2 into cell/mitochondria = V.O2 = Dt (PcO2-PtO2)
=amount of oxygen per unit time disapearing into cells that is entering the mouth from atmosphere (stead state)
Steady state
at rest
-different to exercise where Left hand side of equation will change as consuming/using more oxygen per unit time
Oxygen reservoir at rest
- Advection of O2 in blood (Circulation) (bulk carrying of O2 in fluid/blood)
=Ficks Law = V.O2 = Q (Cao2 - C-vo2) = rate O2 leaves blood = CO/Rate of flow of blood x (difference in O2 content (systemic arterial-mixed venous blood)
(rest= 40% of blood comes back without being used)
-maintain ability to lower amount of O2 reservoir during exercise
-if lower and keep everything else then V.O2 will increase
Diffusion of O2 into cell/mitochondria
- Diffusion of O2 into cell/mitochondria = V.O2 = Dt (PcO2-PtO2)
=amount of oxygen per unit time disappearing into cells that is entering the mouth from atmosphere (stead state)
Dt= diffusing capacity of the tissues
PcO2= partial pressure of systemic capillaries (different capillaries)
PtO2 = partial pressure of tissues
-mitochondria can continue consuming O2 until 1 mmHg or lower
-therefore the partial pressure gradient can be very steep
Which picture best approximates the topology of the human body?
donut
-one hole
